Create StreamDescriptor and associated collection within common

Create StreamDescriptor and associated collection within common
common policy pillar elements.
It moves the code from managerdefault and creates helpers function within
the collection.
It also split the AudioGain in a common volume header and AudioGain class.

Change-Id: I1bb80e4219506f8c9042367085db328d317cb668
Signed-off-by: François Gaffie <francois.gaffie@intel.com>